"How much for an app" is the hardest question in this trade to answer honestly, because the word covers three products that share nothing but a home screen icon.
Three different things called an app
A wrapper around your website. Days to weeks. Cheap, and usually the wrong purchase — if the site works on a phone, an icon adds nothing and the stores increasingly reject these.
A product with one real journey. Ordering, booking, delivery, a service marketplace: accounts, the flow, payments, notifications, working on both platforms. Eight weeks or so with a small team.
A platform. Two sides, money held between them, disputes, an admin back office. Ours took four months including the backend, and that was with people who had built one before.
Most people asking the question want the second and are quoted for the first or the third.
The four things that move the number
Whether money moves inside the app. Payments bring compliance, failure states, refunds and the awkward middle where a payment half-succeeded. It is not a screen; it is a category of work.
Whether there is a server, and whose it is. An app is a client for something. If that something exists and has a decent API, the app is most of the work. If it does not, you are buying two products.
Offline and poor networks. "It should work in the warehouse basement" is one sentence and several weeks. Worth every hour when your users are actually there, and worth cutting when they are not.
How many sides use it. One audience is a product. Two audiences with different journeys, permissions and screens is closer to two products that must agree with each other.
What is not worth paying extra for
A design system before the product has met users. Animations that demo well in a pitch. A second platform if your analytics show ninety percent of your customers on one — check before deciding, not after.
A number you can hold
A first release with one journey working on iOS and Android, tested and submitted to both stores, is around eight weeks of a small team. Meaningfully cheaper usually means one platform, no tests or no backend. Meaningfully dearer usually means more than one journey, which may be right — but it should be a decision you made rather than a surprise you received. For reference, our own first release is $19,000 for eight weeks: one journey, both stores, tests included — the middle of that range rather than the bottom.